1. Field of the Invention
The present invention relates to a high-frequency horizontal deflection/high-voltage generation circuit or apparatus which can be employed in a high-frequency display monitor, a television receiver, etc.
2. Description of Related Art
Concerning the realization of a high-frequency deflecting circuit capable of operating at a high frequency, there have heretofore been made various studies and proposals, which will briefly be reviewed to provide a better understanding of the concept underlying the invention.
The following description will be made by reference to FIGS. 7 and 8 in which FIG. 7 is a schematic circuit diagram showing a circuit configuration of a conventional deflecting circuit known heretofore, and FIG. 8 is a waveform diagram for illustrating operation of the same. Referring to FIG. 7, reference numeral 1 denotes a horizontal switching transistor, 2 denotes a damper diode, 3 denotes a resonant capacitor, 4 denotes a deflecting yoke, 5 denotes a deflecting transformer, 6 denotes an S-shaped capacitor, and numeral 7 denotes a power source.
Now, let's consider the problems encountered in the approaches for implementing the deflecting circuit of the structure mentioned above so that it can operate at a high frequency. Studies concerning the behaviors of such deflecting circuit have been made in the past as well, which will be referenced in the following description.
Referring to FIG. 7 in combination with FIG. 8, when the horizontal switching transistor 1 is turned on, a deflecting current flows through the deflecting yoke 4. Upon turning-off of the horizontal switching transistor 1, a resonant high-voltage pulse (of about 1000 to 1200 volts) which is commonly referred to as the fly-back pulse is generated under the effects of a combined inductance of the deflecting circuit and a capacitance of the resonant capacitor 3. At the end of this fly-back period, the damper diode 2 is turned on, as a result of which a deflecting current of negative polarity flows through the deflecting yoke. Thus, by repetition of the on/off operations of the horizontal switching transistor 1 and the damper diode 2, the horizontal deflecting operation can be realized.
When a predetermined raster amplitude W is to be obtained in the horizontal deflecting operation performed at a scanning frequency F.sub.H in the deflecting circuit shown in FIG. 7, the conditions given by the following expression (1) have to be satisfied. ##EQU1## In the above expression (1), K.sub.1 represents a constant given by the following expression (2): ##EQU2## where E.sub.HT represents a high voltage of a cathode ray tube (also known as the Braun tube).
Further, a deflecting current I.sub.DYPP of the cathode ray tube is given by the expression (3) mentioned below. ##EQU3## where B represents a source voltage,
T.sub.S represents a scanning time, and PA1 L.sub.DY represents the inductance of the deflecting yoke. PA1 P.sub.F represents a loss during the fly-back period, PA1 P.sub.DYS represents loss incurred by the deflecting coil, PA1 P.sub.TRS represents loss in the switching transistor, PA1 R.sub.DY represents resistance of the deflecting yoke, PA1 I.sub.DY represents deflecting current, PA1 R.sub.S represents internal resistance of the switching transistor, PA1 I.sub.PP represents collector current of the switching transistor, PA1 .epsilon. represents an exponent, and PA1 Q represents a so-called Q-value of the resonance. PA1 l represents a magnetic path length, PA1 S represents a cross-sectional area, and PA1 .mu. represents a specific transmittivity.
Referring to FIG. 8 which is a waveform diagram for illustrating operation of the conventional deflecting circuit, relations among the scanning time T.sub.S, horizontal period T.sub.H and the fly-back period T.sub.F are given by the expressions (4), (5) and (6) mentioned below: ##EQU4## where K.sub.2 represents a constant.
A collector voltage V.sub.CP of the horizontal switching transistor 1 making appearance during the fly-back period T.sub.F in the deflecting operation described above can be expressed as follows: ##EQU5##
On the basis of the relations mentioned above, the relation between the inductance L.sub.DY of the deflecting yoke and the scanning frequency F.sub.H can be given by the following expression (8): ##EQU6## where K.sub.3 represents a constant. As can be seen from the above expression (8), the inductance L.sub.DY of the deflecting yoke is in inverse proportion to the second power of the scanning frequency F.sub.H.
On the other hand, the collector voltage V.sub.CP can be given by the following expression (9): ##EQU7##
As is apparent from the above expression (9), the collector voltage V.sub.CP bears no relation to the scanning frequency F.sub.H.
As is apparent from the above analyses, when the collector voltage V.sub.CP is sustained to be constant for ensuring a voltage withstanding capability of the horizontal switching transistor 1, the inductance L.sub.DY of the deflecting yoke will have to be low in reverse proportion to the operating frequency.
Next, the description will turn to the power consumption behavior of the deflecting circuit. In the conventional deflecting circuit shown in FIG. 7, power losses brought about during the scanning period and the fly-back period will be considered separately. For the losses incurred by the deflecting yoke 4 and the horizontal switching transistor 1, the expressions (10), (11), (12) and (13) mentioned below apply. ##EQU8## where P.sub.S represents a loss during the scanning period,
As is apparent from the above, the losses of the horizontal switching transistor 1 in both the scanning period and the fly-back period increase as the frequency becomes higher.
Thus, in order to reduce the losses mentioned above, it is effective to equip the deflecting circuit with measures for decreasing the current of the horizontal switching transistor 1. In more concrete terms it will be required to increase the power source voltage and employ a deflecting yoke having twice to three times as high an inductance value as that of the conventional deflecting yoke in order to suppress the above-mentioned loss.
Next, consideration will be paid to the operation for adjusting the amplitude and correcting a so-called side-pin phenomenon, which are important operations of the horizontal deflecting circuit. Operations for adjusting the amplitude and correcting the side-pin phenomenon can be effectuated by changing appropriately the deflecting current I.sub.DYPP in the expression (1). As the means for changing the deflecting current I.sub.DYPP, there has heretofore been employed a circuit for making variable the source voltage B and a circuit for allowing the inductance L.sub.DY of the deflecting yoke to change. FIG. 10A shows a configuration of the circuit for making variable the source voltage B. In the circuit shown in FIG. 10 in which a power supply of a voltage +B.sub.3 is employed, a voltage drop is caused to take place across the control transistor 153 in order to effectuate the amplitude and side-pin correction as desired. In other words, loss occurs in the control transistor 153. Further, because the crest value of the deflecting voltage +B.sub.1 is not constant as can be seen from FIG. 10B, it is impossible to derive a high output voltage of a constant value from the deflecting circuit. Under the circumstances, a circuit referred to as a diode modulator is generally employed in an effort to make constant the crest value of the collector voltage V.sub.CP. FIG. 11 is a circuit diagram of a typical configuration of such diode modulator circuit. Referring to FIG. 11, the diode modulator is comprised of a first resonant circuit including a deflecting yoke 154 and a resonant capacitor 155, a second resonant circuit composed of a modulator coil 156 and a resonant capacitor 157, and a third resonant circuit composed of a primary winding inductance of a deflecting transformer (also known as the fly-back transformer or FBT in abbreviation) and a distributed capacitance 159 of the deflecting transformer (FBT). Assuming that the resonant circuits mentioned above have the same resonance frequency, the voltage applied to the deflecting yoke 154 is divided between the inductance of the deflecting yoke 154 and that of the modulator coil 156 in proportion to a ratio therebetween. Thus, by changing the source voltage dividing ratio by the control transistor 158, it is possible to realize the amplitude adjustment as well as the side-pin correction. In this operation, the high output voltage of the deflecting circuit will become constant in principle because the collector voltage V.sub.CP is constant. In this way, the high output voltage of the deflecting circuit can certainly be made constant without undergoing adverse influences due to the amplitude adjustment and the side-pin correction. However, even with the diode modulator circuit, it is impossible to avoid the power loss brought about by the control transistor 158. Further, the inductance of the deflecting yoke 154 can not be set at a high value because of the presence of the inductance of the modulator coil 156. Besides, due to the distributed capacitance inherent to the deflecting transformer FBT, a limitation is imposed on the resonance frequency with the result in that the primary inductance (i.e., inductance of the primary winding) of the deflecting transformer can not be set at a high value, which in turn means that the current flowing through the horizontal switching transistor 1 will increase thereby incurring a discharge in that the loss increases. Furthermore, due to the necessity of employing large current elements such as the modulator coil 156, the resonant capacitor 157, the control transistor 158, etc. the prior art circuit is not profitable from the economical standpoint either. In this conjunction, the magnitude of the change K.sub.3 required for the amplitude adjustment and the side-pin correction can be expressed as follows: ##EQU9##
In the above expression (14), L.sub.MOD represents the inductance of the modulator coil 156. As can be seen from the above, the quantity K.sub.3 is restricted by the inductance of the deflecting yoke. For this reason, inductance of the modulator coil 156 has to be set at a low value. In this connection, the inductance L of the deflecting yoke can be expressed as follows: ##EQU10## where n represents the number of turns of the deflecting yoke,
As can be seen from the above expression (15), decreasing the inductance of the deflecting yoke means the number of turns of the deflecting yoke must be decreased correspondingly.
Needles to say, the function of the deflecting yoke is not only to effectuate the scanning operation with the current flowing thorough the coil of n turns but also to suppress color dislocation (so-called convergence characteristic) of the primary colors RGB on the phosphor screen of the cathode ray tube while ensuring generation of the pictures with possibly minimum distortion. In this conjunction, it is noted that a reduced number of turns of the coil of the deflecting yoke makes it difficult to set an optimal distribution of the magnetic flux or field.
In many examples of the high-frequency deflecting devices known heretofore, the high-voltage generating circuit is implemented separately from the deflecting circuit in order to evade the influence of the former on the latter, the reasons for which may be explained by the facts that a multi-scan system for causing the operating frequency to follow automatically the video signal, a device for allowing the user to perform the adjustment of amplitude and so forth is adopted, as a result of which difficulty is encountered in deriving a stable high voltage from the deflecting pulse. FIG. 9 is a circuit diagram showing schematically a configuration of a high-frequency deflecting circuit known heretofore in which the deflecting circuit and the high-voltage generating circuit are implemented separately from each other. In FIG. 9, reference numeral 8 denotes a deflecting circuit and 9 denotes a high-voltage generating circuit, wherein the deflecting circuit 8 and the high-voltage generating circuit 9 operate independent of each other with the high-voltage generating circuit 9 being provided with a facility detecting a high voltage for thereby controlling the high-voltage generating circuit so that the high-voltage output can be stabilized.